Table 1

Operational definitions used in study

Training sessionTeam training that involved physical activity under the supervision of the coaching staff
MatchCompetitive or friendly match against another team
InjuryAny physical complaint sustained by a player that resulted from a football match or football training and led to the player being unable to take full part in future football training or match play
Ankle injuryInjury to the tibiotalar and the inferior tibiofibular joints as well as the surrounding stabilising connective soft tissue (ie, joint capsules and ligaments) of these joints and the overlying skin
Slight/minimal injuryInjury causing 0–3 days lay-off
Mild injuryInjury causing 4–7 days lay-off
Moderate injuryInjury causing 8–28 days lay-off
Severe injuryInjury causing >28 days lay-off
Traumatic injuryInjury with sudden onset and known cause
Overuse injuryInjury with insidious onset and no known trauma
ReinjuryInjury of the same type and at the same site as an index injury occurring within 2 months after return to full participation from the index injury
Non-contact injuryInjury occurring without contact with another player or object
Dominant legPreferred kicking leg
Foul playViolation of the laws of the game according to the match referee
Injury rateNumber of injuries per 1000 player hours ((Σ injuries/Σ exposure hours)×1000)
Injury burdenNumber of lay-off days per 1000 player hours ((Σ lay-off days/Σ exposure hours)×1000)